Technical Manual Technical Description
© SPECTRA ENGINEERING 2006 Revision 4.2.3
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3.17.4.3 Configuration
The configuration procedure for the Variable tone encoder consists of setting
up the software and adjusting the noise circuit for maximum range. The
configuration screen is entered via the menu system using options ‘C’ for
configuration, then ‘E’ for encoder and then ‘1’ for Variable tone encoder.
When the Variable tone encoder is initially enabled it is configured with the
system defaults as shown above, or a previously configured Variable tone
voting law. The user can change the number of Variable tone levels, the
Variable tone decision points and tone frequencies. If the user decides to
change any setting all the Variable tone settings will need to be entered.
The number of levels refers to the number of decision points once the mute is
opened. Level 0 is the receiver signal level when the mute just opens; use the
appropriate units for the decision point. The units for the Variable tone
decision points can either be in microvolts (uV) or decibels (dBm).
3.17.4.4 Adjustment
The process for adjusting the noise measurement circuit for range is to inject
a signal of about 0.6uV (or approximately -111.4 dBm) into the receiver and
measure the filtered noise signal on the pad between R131 and C67. The
voltage should be around 0.7V, use variable resistor RV6 to adjust the gain.
The Variable tone encoder tone level can be adjusted using variable resistor
RV1. This is typically –20dBm tone level.
The line output level is adjusted using variable resistor RV4, for the desired
level. This is typically –10dBm audio level.
3.17.4.5 Calibration
Once the board has been configured for Variable tone voting, calibration is
performed using screen prompts in the calibration menu. Enter using the
menu system option ‘R’ for calibration then ‘N’ for noise-floor
measurements. The user will then be prompted to adjust the receiver signal to
match the calibration points.
After calibrating the noise floor decision points, the frequency compensation
adjustments will need to be performed. This is done through the menu system
using options ‘R’ then ‘C’. The user will then be prompted to turn off the
receiver signal source to initiate the calculations.
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